A novel proton exchange membrane prepared from imidazole metal complex and Nafion for low humidity

A simple MOF constructed using Pb(II) with strong polarizing force: a filler of Nafion membrane to increase proton conductivity

Metal-organic frameworks (MOFs) are promising competitive candidates as fillers for Nafion proton exchange membrane (PEM). Increasing efforts have been made to explore methods for synthesizing MOF fillers and the mechanism by which MOF doping improves the proton conductivity (σH+) values of composite membranes. In this study, a Pb(II) cation with strong polarizing force was selected for the hydrothermal reaction with a simple sulfoterephthalate ligand (H3L). Pb-MOF [Pb2L(OH)]n was obtained, which was constructed using Pb-O layers and deprotonated sulfoterephthalate L3- and exhibited good thermal and water stability. Different amounts of Pb-MOF particles were doped into Nafion to fabricate Pb-MOF/Nafion-x composite membranes, which were characterized using SEM, PXRD, IR spectroscopy, TGA, and other methods. It was found that doping Pb-MOF can apparently improve the water absorbability and thermal stability of the composite membrane. The σH+ of the Pb-MOF/Nafion-7 composite membrane was the highest and 2.14 times that of the pure Nafion membrane at 353 K. The higher proton conduction properties may be explained by the strong polarization force, and Pb(II) cations on the surface of Pb-MOF can decrease the bond energy of the O-H bond of absorbed water molecules and increase the acidity of the composite membrane. The phenomena in this study and our previous study confirm that acidity is the most important factor in favor of proton conductivity.

Resistance-Based Lateral Flow Immunosensor with a NFC-Enabled Smartphone for Rapid Diagnosis of Leptospirosis in Clinical Samples

Leptospirosis is one of the most life-threatening tropical diseases caused by pathogenic Leptospira. To date, a diagnostic device that offers rapid and sensitive detection of leptospires has been still in demand for proper treatment to reduce the mortality rate. Herein, we create a resistance-based lateral flow immunosensor diagnosis device (R-LFI) that integrates near-field communication (NFC) with a portable smartphone for leptospiral detection in clinical samples. A specific monoclonal antibody against the pathogen was coated on a nitrocellulose membrane (NCM) where the test line was collocated. Two electrodes with a sandwich-like configuration were installed employing a conductive double-sided adhesive tape and connected with a NFC smartphone-based detection system. A half-sandwich immunocomplex formation induced high proton conduction, resulting in a considerable decrement in resistive response. The performance of the R-LFI sensor was evaluated using recombinant LipL32 (rLipL32), Leptospira interrogans, and clinical samples. The R-LFI device exhibited linear responses toward rLipL32 protein in phosphate buffer and L. interrogans-spiked healthy human serum samples within the concentration ranging from 1 to 1000 ng mL^-1 (limit of detection (LOD): 0.29 ng mL^-1) and from 10⁴ to 10⁶ cell mL^-1 (LOD: 4.89 × 10³ cell mL^-1), respectively. Our R-LFI sensor successfully detected L. interrogans-positive clinical samples as confirmed by polymerase chain reaction (PCR). This platform offers high specificity, selectivity, simplicity, miniscule sample volume, and no labeling element requirement. These desirable features make it particularly suitable for countries where medical facilities and resources are limited.

Enhancing Proton Conductivity of Nafion Membrane by Incorporating Porous Tb-Metal-Organic Framework Modified with Nitro Groups

A rigid carboxylate ligand with a nitro functional group was selected to coordinate with Tb(III) cation, and Tb-MOF ({[Tb₄(L)₄(OH)₄(H₂O)₃]·8H₂O}_n, H₂L = 2-nitroterephthalic acid) with large porous and excellent hydrophilicity was obtained successfully. The obtained Tb-MOF was filled into the Nafion matrix to improve its proton conduction performance. The Tb-MOF/Nafion composite membrane was characterized by PXRD, IR, and thermogravimetry (TG) and for water uptake, area swelling, and proton conductivity. The activity energy, E_a, value of the composite membrane, which is a very important factor affecting the proton conduction performance of the membrane, was fitted and calculated. It was revealed that Tb-MOF can improve the proton conductivities of composite membranes, and the improvement degree and E_a value were both affected by Tb-MOF content. When Tb-MOF content was 5%, the proton conductivity of the composite membrane was 1.53 × 10^-2 S·cm^-1 at 100% RH and 80 °C, which is 1.81 times that of the pure Nafion membrane. A MOF containing a nitro functional group was first doped into Nafion in this study and exhibited excellent performance for improving composite membrane proton conductivity. This study will provide a valuable reference for designing different functionalized MOFs to promote the proton conductivities of proton exchange membranes.

Enhanced proton conductivity of Nafion-azolebisphosphonate membranes for PEM fuel cells

Azolebisphosphonates were prepared and used as dopants to obtain new Nafion doped membranes, which exhibited higher proton conductivities than that of Nafion.

Site-specific electronic structure of imidazole and imidazolium in aqueous solutions

The electronic structures of aqueous imidazole and imidazolium solutions are studied in an atom- and site-specific fashion using soft X-ray spectroscopy.

Two-Dimensional Zeolitic Imidazolate Framework/Carbon Nanotube Hybrid Networks Modified Proton Exchange Membranes for Improving Transport Properties

Metal-organic framework (MOF)/polymer composite proton exchange membranes (PEMs) are being intensively investigated due to their potentials for the systematic design of proton-conducting properties. However, the development of MOF/polymer composite PEMs possessing high selectivity remains exceedingly desirable and challenging for practical application. Herein, two-dimensional (2D) zeolitic imidazolate framework (ZIF-8)/carbon nanotube (CNT) hybrid cross-linked networks (ZCN) were synthesized via the rational design of the physical form of ZIF-8, and then a series of composite PEMs were prepared by hybridizing ZCN with sulfonated poly(ether ether ketone) (SPEEK) matrix. The effect of the incorporation of zero-dimensional (0D) raw ZIF-8 nanoparticles and 2D ZCN on the proton conduction and methanol permeability of the composite membranes was systemically studied. Benefiting from the morphological and compositional advantages of ZCN, the SPEEK/ZCN composite membranes displayed a significant enhancement in proton conductivity under various conditions. In particular, the proton conductivity of SPEEK/ZCN-2.5 membrane was up to 50.24 mS cm^-1 at 120 °C-30% RH, which was 11.2 times that of the recast SPEEK membrane (4.50 mS cm^-1) and 2.1 times that of SPEEK/ZIF membrane (24.1 mS cm^-1) under the same condition. Meanwhile, the methanol permeability of the SPEEK/ZCN composite membranes was greatly reduced. Therefore, novel MOF/polymer composite PEMs with high selectivity were obtained. Our investigation results reveal that the proton conductivity and methanol permeability of the MOF/polymer composite membranes can be effectively tailored via creating more elaborate superstructures of MOFs rather than altering the chemical component. This effective strategy may provide a useful guideline to integrate with other interesting MOFs to design MOF/polymer composite membranes.

Novel Composite Proton Exchange Membrane with Connected Long-Range Ionic Nanochannels Constructed via Exfoliated Nafion-Boron Nitride Nanocomposite

Nafion-boron nitride (NBN) nanocomposites with a Nafion-functionalized periphery are prepared via a convenient and ecofriendly Nafion-assisted water-phase exfoliation method. Nafion and the boron nitride nanosheet present strong interactions in the NBN nanocomposite. Then the NBN nanocomposites were blended with Nafion to prepare NBN Nafion composite proton exchange membranes (PEMs). NBN nanocomposites show good dispersibility and have a noticeable impact on the aggregation structure of the Nafion matrix. Connected long-range ionic nanochannels containing exaggerated (-SO₃^-)_n ionic clusters are constructed during the membrane-forming process via the hydrophilic and H-bonding interactions between NBN nanocomposites and Nafion matrix. The addition of NBN nanocomposites with sulfonic groups also provides additional proton transportation spots and enhances the water uptake of the composite PEMs. The proton conductivity of the NBN Nafion composite PEMs is significantly increased under various conditions relative to that of recast Nafion. At 80 °C-95% relative humidity, the proton conductivity of 0.5 NBN Nafion is 0.33 S·cm^-1, 6 times that of recast Nafion under the same conditions.

Novel Composite PEM with Long-Range Ionic Nanochannels Induced by Carbon Nanotube/Graphene Oxide Nanoribbon Composites

In the current study, carbon nanotube/graphene oxide nanoribbon (CNT/GONR) composites were obtained via a chemical "unzipping" method. Then novel CNT/GONR Nafion composite proton exchange membranes (PEMs) were prepared via a blending method. The CNT/GONR nanocomposites induce the adjustment of (-SO₃^-)_n ionic clusters in Nafion matrix to construct long-range ionic nanochannels and keep the activity of ionic clusters at the same time. This dramatically promotes the proton transport of the CNT/GONR Nafion composite PEMs at low humidity and high temperature. The proton conductivity of the composite PEM with 0.5 wt % CNT/GONR is as high as 0.18 S·cm^-1 at 120 °C and 40%RH, nine times of recast Nafion (0.02 S·cm^-1) at the same conditions. The 1D/2D nanostructure of CNT/GONR nanocomposite also contributes to restrain the methanol permeability of CNT/GONR Nafion. The composite PEM shows a one-order-of-magnitude decrease (2.84 × 10^-09 cm²·s^-1) in methanol permeability at 40 °C. Therefore, incorporation of this 1D/2D nanocomposite into Nafion PEM is a feasible pathway to conquer the trade-off effect between proton conductivity and methanol resistance.

Nafion-Initiated ATRP of 1-Vinylimidazole for Preparation of Proton Exchange Membranes

Nafion is one of the most widely investigated materials applied in proton exchange membranes. Interestingly, it was found that Nafion could serve as a macroinitiator to induce atom transfer radical polymerization (ATRP) on its C-F sites. In this study, poly(1-vinylimidazole) was selectively bonded on the side chains of Nafion via the Nafion-initiated ATRP process, which was confirmed by the measurements of (1)H/(19)F nuclear magnetic resonance spectra, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, differential scanning calorimeter and matrix-assisted laser desorption ionization-time-of-flight/time-of-flight mass spectrometry. The as-prepared Nafion-co-poly(1-vinylimidazole) (Nafion-PVIm) membranes, with tunable loading amount of imidazole rings, presented greatly enhanced proton conductivity and methanol resistivity due to their well-controlled chemical structures. Especially, chemically bonding PVIm with Nafion chains endowed the Nafion-PVIm membranes with high stability in proton conductivity. For the first time, we revealed the great potentials of the Nafion-initiated ATRP process in developing high-performance proton exchange membranes.